Previous research has looked at the harmful effect of organophosphate pesticides -- chemicals that target the nervous system -- on adult agricultural workers. This new study looked at children living in an agricultural area where the organophosphates are used.

"This is the first evidence suggesting that children exposed to organophosphates have poorer lung function," said study senior author Brenda Eskenazi, a professor of epidemiology and of maternal and child health at the University of California, Berkeley.

For this study, researchers measured levels of organophosphate pesticides in urine samples collected on five occasions from 279 children in California's Salinas Valley between the ages of 6 months and 5 years.

The area is an agricultural hub, producing lettuce, grapes, orchids and more for much of the nation.

At age 7, the children were given a test to assess their ability to take deep breaths and then expel the air. Each 10-fold increase in organophosphate levels was associated with about an 8 percent decrease in the amount of air a child could exhale, the study found.

That decline is similar to that caused by exposure to secondhand smoke from mothers, according to the study published Dec. 3 in the journal Thorax.

The findings remained constant even after the researchers accounted for other factors that could affect the children's lung health, including smoking by their mothers, air pollution, or mold or pets in the home.

Raanan said the study adds exposure to organophosphate pesticides to the growing list of environmental exposures -- including air pollution, indoor cook-stove smoke and tobacco smoke -- that could harm the developing lungs of children.

"Given they are still used worldwide, we believe our findings deserve further attention," she added.

Although use of organophosphates is still widespread, it has decreased considerably in the United States since the study began in 2000, the researchers said in background notes.

While the study found an association between pesticide exposure and respiratory decline, it didn't prove a direct cause-and-effect relationship.